Lead alloy



. 6, 1932. R. s. DEAN LEAD ALLOY Original Filed June 29. 1928 Y and more particularly Patented Dec. 6, 1932 UNITED STATES PATENT OFFICE REGINALD S. DEAN, 0F WASHINGTON, DISTRICT 0F COLUMBIA, ASSIGNOB T0 WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW- YORK LEAD ALLOY Original application led June 29, 1928, Serial No. 289,145. Divided and this application led Hay 24, 1930. Serial No. 455,190.

This invention relates to lead alloys, articles made therefrom, and methods of producing and/or treating such alloys and articles, to alloys of lead and calcium, extruded articles made therefrom, and methods of producing and/or treating such alloys and articles, and is a division of my co ending application Serial No. 289,145, filed une 29, 1928.

An object of the invention is to provide alloys of lead and calcium having some or all of the properties of extreme hardness, high tensile strength, great resistance to failure from fatigue, large percentage elongation, excellent resistance to corrosion, and great stability at atmospheric temperatures.

Another object of the invention is to provide articles made of alloys of lead and calcium, particularly electrlcal cable sheaths made of such alloys.

Additional objects of the invention are to provide simple, effective, and expeditious methods of producing and/or treating alloys of lead and calcium and articles made from such alloys resulting in and having desired physical and mechanical properties.

In accordance with the general features of the invention as embodied in one specific form thereof, a quantity of calcium is alloyed with a suiiici'ent quantity of lead to produce an! alloy containing less than 1% calcium and the alloy caused to solidify. The solidified alloy is heated at a temperature sufficiently high and for a sufficiently long period of time to cause substantially all of the resulting solute constituent to enter solid solution in the lead, and the alloy is then cooled from an elevated temperature at a suiiciently rapid rate to cause some of the solute constituent to remain in the lead in the form of a supersaturated solid solution, after which the alloy is caused to assume va more stable state by aging. I-n the manufacture of articles, such as cable sheaths, from an alloy of the type just described, an article may be formed therefrom and then the formed article subjected to the above outlined heating, cooling and aging operations, or else the alloy may be first reduced to the form of a solid solution and an article produced therefrom while the alloy is hot, after which the hot article is cooled and aged in the manner described above.

The above described and other objects and features of the invention will be apparent from the following detailed description of one embodiment of the invention, taken in connection with the accompanying drawing, in which Fig. 1 is an equilibrium diagram of the lead-rich end of the lead-calcium system;

Fig. 2 is a diagram showing the comparative tensile strengths of alloys treated in accordance with this invention and alloys not so treated, and

Fig. 3' is al diagram similar to that shown in Fig. 2 showing the comparative percentage elongations of treated and untreated alloys.

Referring now to Fig. 1 of the drawing, the curves shown therein represent the loci of the points at which transformations in the physical conditions of lead-rich alloys of lead and calcium occur. In the diagram shown in Fig. 1, the temperatures at which the transformations occur are plotted as ordinates and the percentage compositions of the alloys in which the transformations occur are plotted as abscissae. The curve ABC in the diagram is a liquidus curve from which the melting points of the various lead-calcium alloys may be obtained, while the curve DE represents the solubility in lead of the solid solute constituent separating out with the lead when the lalloys solidify. From an examination of the diagram it will be seen that the solubility of the solid solute constituent in lead varies with the temperature, the solid lead dissolving about 0.1% of the calcium at 380 C. and less than 0.02% at room temperature or lower temperatures. In accordance with this invention, advanta e is taken of the above described characteristlcs of leadrich alloys of lead and calcium to produce alloys having enhanced properties and to produce articles, such as cable sheaths, from these alloys.

Although it is not known with certainty just what the solution of the lead and the solute constituent comprises, it is believed that the calcium combines chemicall with a part of the lead to form a compoun having the formula PbaCa which enters solid solution in the remainder of the lead and septI o i rates out as a distinct constituent under cer-\ tain conditions. In any event, whether or not such a compound is found, the calcium, either combined or uncombined chemically with a part of the lead, enters into solid solution in the lead. The theory upon which the processes described below are based 1s the same regardless of Whether the calcium is free or combined and it is to be understood, therefore, that in the following description and annexed claims when it is stated that the solute constituent or the calcium is caused to enter solid solution in the lead, these terms are intended to mean either combined or uncombined calcium as the case may actually be.

In practicing one method of producmg alloys in accordance with the invention, a quantity of calcium falling within the range bounded by the maximum amount of calcium which will enter solid solution in. lead at any temperature at which the resulting alloy is a solid and the amount of calcium which will be retained in solid solution in lead at room temperature (0.02% to 0.1% calcium) is alloyed with lead and the resulting alloy caused to solidify. The solid allo)7 heated at a temperature suiciently high to cause the calcium to enter solidsolution in the lead, which temperature may 'be determined by referring to the diagram shown in Fig. 1 of the drawing, and the heating is continued until substantially all of the calcium has entered into a substantially homogeneous solid solution in the lead. The alloy v is then cooled from an elevated temperature at a rate ysutliciently rapid to insure the retention of some of the calcium in the lead in the form of a supersaturated solution, after which the alloy is caused to assume a more stable state by aging. The percentage of calcium employed and the temperatures at which the heating, cooling and aging steps are practiced depend upon the characteristics desired in the finished product and may be determined by reference to Figs. 2 and 3 of the drawing. e

Referring now to Fig. 2 of the drawing, which illustrates the comparative tensile strengths of alloys treated in accordance with the invention and alloys not so treated, the curve F represents the tensile strength of the various alloys, whose compositions are indicated as abscissae, which have been heated at atemperature of approximately 320o C. until a substantially homogeneous solid solution was produced and quenched from the temperature of 310 C. to room temperature and aged at room temperature, while the curve G illustrates the tensile strengths of corresponding alloys which have been slowly cooled from 310 C. to room temperature so that practically no supersaturation of the solution of the solute constituent in the lead is thenresults. It will be seen by reference to Fi 2 that t-he alloys treated in accordance wit the invention possess considerably greater tensile strength than is possessed by the alloys not so treated, and also that the tensile strength of the treated alloys .varies with the composition thereof, the tensile strength reaching a high value when an alloy containing about 0.1% calcium is employed. From this it will be evident that great tensile strength in the treated alloys results when the maximum amount of calcium which will enter solid solution in lead at any temperature at which the resulting alloy is a solid is employed.

Referring now to Fig. 3 of the drawing which illustrates the comparative percentage elongations of alloys treated in accordance with the invention and alloys not so treated, the curve H represents the percentage elongations in six inches of alloys which have been formed into a solid solution, reduced to a supersaturated solid solution and aged, while the curve I represents the percentage elongations of corresponding alloys which have been produced in such a manner that very little, if any, supersaturation ofthe solid solution results. As a general rule, the percent-l I age elongation of metals decreases rapidly with increased tensile strength and it might be expected that lead-calcium alloys of increased tensile strength would exhibit low percentage elongations. However, from an examination of these curves it will be apparent that the percentage elongations of the treated alloys, while less than those obtained in the untreated alloys, are not suliiciently less to materially decrease the usefulness of the treated alloys for the manufacture of articles, such as cable sheaths. As in the case of the tensile strength, a high percentage elongation results when the `maximum amount of calcium is employed which will enter solid solution in lead at any temperature at which the resulting alloy is a solid, namely about 0.1% calcium.

If an alloy of a particular tensile strength and percentage elongation is desired these characteristics may be obtained by employing an alloy having -the composition corresponding to the particular characteristics desired. For instance, if it is desired to produce an alloy having a tensile strength of about 7000 pounds per square inch and a percentage elongation of about 40%, approximately 0.1% calcium is alloyed with lead and the resulting alloy is reduced to a solid state. The solid alloy is then heated at a temperature bet-Ween 310 and 325 C., which is the temperature necessary to cause this quantity of calcium to enter solid solution in lead, and the heating is continued until substantially all of the calcium has entered solid solution in the lead. If great tensile strength is desired, the alloy is quenched from a temperature of about 310 C. to room temperature by immersing the alloy in water, and the alloy is caused to assume a morestable state by aging the alloy at a temperature at which little agglomeration occurs, room temperature having proven to be a very satisfactory temperature at which to conduct the aging step. By the above described process an alloy is produced consisting of a matrix of lead throughout which are substantially uniformly dispersed a large number of minute particles containing calcium and it is believed that the enhanced properties which such alloys possess result from the wide dispersion of these particles and the extreme minuteness of the particles. It is important, therefore, that the aging step be carried on at a temperature sufficiently low so that little agglomeration of the finely dispersed particles results, and it has been found that little agglomeration occurs when the alloy is aged ata temperature below 150 C.

By practicing the above outlined method, alloys having very desirable properties may be produced. For instance, alloys having a tensile strength from 4000 to 7000 pounds r square inch, a percentage elongation of from 25 to 40% and a fatigue limit of from 800 to 1900 pounds per square inch, may be obtained by following the above outlined process. Other advantageous properties of such alloys are their resistance to chemical corrosion and their extreme stability of physical pro erties at atmos heric temperatures.

The :ibove enumerate properties of alloys *A produced in accordance with this invention are very desirable in extruded articles, particularly sheaths for electrical cables, and the above described process provides an excellent means for producing such articles. For instance, in the manufacture of electrical cable sheaths, a lead-calcium alloy of the composition necessary to give the tensile strength,

ercentage elongation, etc., desired in the finished sheath is produced, and the solid alloy then heated and extruded -in the form of a sheath surrounding an electrical cable under such conditions that the alloy making up the sheath as extruded will be in the form of a substantially homogeneous solid solution. The alloy is then cooled at a rate sufficiently rapid to insure the retention of some of the solute constituent in a supersaturated solution in the lead and the sheath then aged to cause a dispersion of a solute constituent throughout the lead in the form of minute particles. Electrical cable sheaths made in accordance with the invention have proven to have characteristics far superior to those made of other alloys commonly used in the manufacture of cable sheaths, and consequently sheaths made in accordance with the invention will be much more effective under service conditions than those heretofore known to the art.

It is, of course, to be understood that the methods outlined above and the articles and alloys produced by practicing these methods are merely illustrations of useful embodiments of the invention and the invention is limited only by the scope of the annexed claims.

What is claimed is:

1. A method of producing extruded lead alloy articles, which comprises alloying less than 1% calcium with lead by heating the ingredients, extruding the resulting alloy in theform of a solid solution into an article, quenching the article to reduce the alloy to a supersaturated solid solution, and immobilizing the solid solution.

2. A method of producing electrical cable sheaths, which comprises alloying from 0.02% to 0.1% of calcium with lead by heating the ingredients, extruding the resulting alloy in the form of a solid solution into a sheath,

quenching the alloy to reduce the alloy to a supersaturated solid solution, and immobilizing the solid solution.

3. An electrical cable sheath comprising an age-hardened alloy of lead and calcium containing from 0.02% to 0.1% calcium.

4. A method of producing lead alloy articles, which comprises alloying less than 1% of calcium with lead, heating the alloy to bring the resulting alloy into the form of a solid solution at an elevated temperature,

shaping the solid solution while at said elevated temperature into the form of the article, quenching the article to form a supersaturated solid solution, and aging the article at a temperature below 150 C. f 5. An electrical cable sheath comprisin an alloy of lead-calcium wherein less than 1 o of calclum is present in supersaturated solid solution.

6. An electrical cable sheath comprising an alloy of lead-calcium containing less than 1% of calcium, which has been heated to between 310 C. and 825 C. and quenchedv to a temperature below 150" C.

7. An electrical cable sheath comprising an alloy of lead with from 0.02% to 0.10% calclum, which 'nas been heated to between 310 C. and 325 C. and quenched to a tempera-ture below 150 C.

, In witness whereof, I hereunto subscribe my nam-e this 15th day of May A. D., 1930.

REGINALD S. DEAN. 

